Method for preparing a polycarboxylic composition comprising an electrochemical oxidation stage of a monosaccharide composition

ABSTRACT

A method for preparing a polycarboxylic composition, includes a stage in which a monosaccharide composition undergoes an electrochemical oxidation treatment carried out in the absence of sodium hypochlorite and in the presence of a) an amine oxide and b) a carbon-based anode. Preferably, the anode is selected from the group comprising carbon felt and granular active carbon. The electrochemical oxidation treatment can be carried out advantageously at a pH, preferably of between 11.5 and 14. The method makes it possible to obtain novel products, especially 2-carboxy-2, 3, 4-trihydroxypentane-dioicious acid, the salts and derivatives thereof.

This is a 371 National Stage application of International applicationno. PCT/FR2003/02702, filed Sep. 12, 2003, which claims priority toFrench application no. 02/11546, filed Sep. 18, 2002. The entirecontents of the above-referenced applications are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

A subject-matter of the present invention is a novel method forpreparing polycarboxylic compositions, said method comprising a stage ofelectrochemical oxidation of a monosaccharide composition carried outunder specific conditions.

It also relates, as novel materials, to some of the polycarboxyliccompositions that are obtained by said method.

In addition, the present invention is directed to the use of saidpolycarboxylic compositions in certain industries, such as, for example,those of detergents and cleaning agents, of water treatment or ofhydraulic binders or the food or pharmaceutical industries.

BACKGROUND OF THE INVENTION

In those industries, it is common to use materials resulting fromproducts of natural or synthetic origin which are of polymeric ormonomeric structure and which comprise at least two carboxylicfunctional groups. All or part of these functional groups can exist ineither the “free acid” (COOH) form or other forms, in particular in theform of associated salts, such as alkali metal or alkaline earth metalsalts. These materials, which can be described as “polycarboxylates”,can be used in particular as chelating or sequestering agents formetals, detergency builders or cobuilders, or agents which delay thesetting of hydraulic binders but also as stabilizing, structuring,dispersing, disintegrating or stripping agents for compositions of anynature and destination.

They can consist of natural products derivatives, such as poly- andmonosaccharides, in particular of starch derivatives or ofstarch-hydrolyzed products.

They can be, inter alia:

-   -   carboxyalkylated derivatives of starch hydrolysates,    -   glucuronyl-arabinarates or glucuronyl-glucarates, obtained from        starch hydrolysates,    -   glucuronyl-glucaric acid, glucaric acid or mannaric acid,        obtained respectively from maltitol, sorbitol or mannitol,        the preparation and the uses of such polycarboxylates resulting        from natural products being disclosed in particular in patents        WO 95/02614, EP 780 399 and EP 798 310 on behalf of the        Applicant Company and, for example, in patent EP 656 051.

Other monomeric or polymeric polycarboxylates result from products ofsynthetic or natural origin that are of non-saccharide nature, such as,for example:

-   -   dicarboxylic acids, such as tartaric acid, succinic acid or        glutaric acid,    -   tricarboxylic acids, such as citric acid or nitrilotriacetic        acid (“NTA”),    -   tetracarboxylic acids, such as ethylenediamine-tetraacetic acid        (“EDTA”),    -   (co) polymers of ethylenic carboxylic acids, such as, for        example, polyacrylates,        the uses of such polycarboxylates resulting from products of        non-saccharide nature being, inter alia, disclosed in patents FR        2 657 601, FR 2 735 788, WO 91/00901, EP 565 266, EP 605 318, EP        650 941 or EP 972 825.

In view of the current restrictions for the protection of the human lifeand the environment, it is advisable to have available polycarboxylatesresulting from renewable products of natural origin.

For approximately a decade, numerous studies have focused on severalpolycarboxylates such as glucaric acid and its salts.

The abovementioned patent EP 656 051 discloses the preparation ofphosphate-free detergents based on zeolites and/or on lamellar silicatescomprising, as complexing agents, polyhydroxydicarboxylic acids orpolyhydroxydicarboxylic acid salts comprising from 4 to 6 carbon atomsand at least 2 hydroxyl groups per molecule, such as, in particular,sodium glucarate and sodium galactarate.

The abovementioned patent EP 798 310, published on behalf of theApplicant Company, discloses, in its Example 1, the preparation of acomposition comprising 33% of glucaric acid in the form of its sodiumsalt and 67% of sodium chloride, with the absence of products from theoveroxidation of glucaric acid. This composition, which has high contentof NaCl, is obtained by oxidation of sorbitol by sodium hypochlorite(NaOCl or “bleach”) in the presence of a catalyst composed of a binaryor tertiary alkyl nitroxy, such as 2,2,6,6-tetramethylpiperidinyloxy or“TEMPO”.

More recently, other studies have been described in the paper by J. F.Thaburet et al. entitled “TEMPO-mediated oxidation of maltodextrins andD-glucose: effect of pH on the selectivity and sequestering ability ofthe resulting polycarboxylates”, Carbohydrate Research, 330 (2001), pp.21-29.

These studies have shown that the oxidation of glucose or sorbitol inthe presence of TEMPO and NaOCl was particularly difficult to control.Nevertheless it was possible to obtain a good yield (90%) of glucaricacid under very specific conditions (including a pH of 11.7 and thenecessary presence of sodium bromide NaBr).

Furthermore, this document shows that, depending on the number ofequivalents of NaOCl employed, the glucaric acid synthesis results inthe preferential coproduction:

-   -   either of gluconic acid, i.e. of the monocarboxylic acid        corresponding to glucaric acid,    -   or of other dicarboxylic acids but which are small, namely        tartaric acid and oxalic acid.

The authors believe that the coproduction of these last two acids is dueto the oxidative decomposition of the monosaccharide (glucose, sorbitol)at two breakdown on the molecule, namely a) between the C-4 and C-5carbon atoms and b) between the C-2 and C-3 carbon atoms.

More recently still, other pathways for the decomposition of glucaricacid have been suggested, as an attempt to explain the coproduction ofmeso-tartaric acid or of D-tartaric acid during the oxidation of glucoseto glucaric acid in the presence of NaOCl, NaBr and TEMPO.

These decomposition pathways, hypothetical or otherwise, are describedin the very recent paper by M. Ibert et al. entitled “Determination ofthe side-products formed during the nitroxide-mediated bleach oxidationof glucose to glucaric acid”, Carbohydrate Research, 337 (2002), pp.1059-1063.

In any case, in view of the above there is a number of drawbacks in thepreparation of dicarboxylic acid, such as glucaric acid, from amonosaccharide, such as glucose, which may be optionally hydrogenated(sorbitol), and in particular:

-   -   the use of sodium hypochlorite, which is not desirable because        of the current restrictions for the protection of human life and        the environment,    -   the possible use of NaBr, that is not desirable given its        capacity to generate halogenated entities,    -   the need to closely monitor and control the reaction parameters,        such as the pH and the concentration of NaOCl, in order to        obtain a minimum or acceptable yield of desired product,    -   the significant and undesired coproduction either of not        profitable materials (NaCl) or monocarboxylic materials        (gluconic acid and its salts) or dicarboxylic materials (oxalic        and tartaric acids and their salts). These materials have a        (very) greatly reduced molecular weight due to decomposition.        They also have few (tartaric acid) or no (oxalic acid) OH        groups. The presence of these materials reduces the properties,        in particular the chelating or sequestering properties, of the        glucaric acid composition.

In addition to these problems regarding the generation of decompositionproducts, the oxidation of mono-saccharides with TEMPO and sodiumhypochlorite does not make it possible to obtain materials having threecarboxylic functional groups, as is the case, with polycarboxylatescommonly used in industry, such as citric acid and citrates.

SUMMARY OF THE INVENTION

Therefore there is a need for a means capable of eliminating theabovementioned disadvantages and in particular a means which, startingfrom monosaccharides, makes it possible a) to efficiently preparecompositions having a high content of polycarboxylic materials and inparticular a high content of dicarboxylic materials, such as glucaricacid and its salts, and b) optionally to have novel compositions basedon dicarboxylic materials and tricarboxylic materials. All thesecompositions are able to be advantageously used in the industries andfor the purposes mentioned previously.

Thanks to the present invention, there will be no need to use sodiumhypochlorite and to rigorously control the pH of the reaction.

MORE DETAILED DESCRIPTION

After numerous research studies, it is to the credit of the Applicant tohave found, that such a means consists in using a specific method, i.e.an electrochemical oxidation treatment, carried out under specificconditions, in particular related to the specific nature of the anodeused for the oxidation.

More specifically, a subject matter of the present invention is a methodfor preparing a polycarboxylic composition, characterized in that itcomprises a stage in which a monosaccharide composition undergoes anelectrochemical oxidation treatment carried out in the absence of sodiumhypochlorite and in the presence a) of an amine oxide and b) of acarbon-based anode.

The term “polycarboxylic composition”, within the meaning of the presentinvention, is understood as any composition comprising at least 50% byweight of one or more products chosen from the group consisting ofdicarboxylic acids, tricarboxylic acids and the salts and thederivatives of said acids, this percentage being expressed as total dryweight of this (these) product(s) with respect to the total dry weightof said composition.

The term “monosaccharide composition” is understood as any compositioncomprising at least 50% by weight of one or more monosaccharide(s), thispercentage being expressed as total dry weight of monosaccharide(s) withrespect to the total dry weight of said composition.

This percentage can advantageously be at least 80% and can reach 100%.

The dry matter content of the monosaccharide composition can be within avery wide range, preferably between 0.1 and 50%, depending on possibleeconomic or technical limitations, such as the optimization of theviscosity and the thermal characteristics of the reaction medium.

This dry matter (DM) can comprise at least one monosaccharide chosenfrom the group consisting of aldoses, ketoses and their respectivederivatives, with the exception of those in which the hemiacetalfunctional group carried by the carbon in the position 1 (Cl) has beenprotected against oxidation by amination, esterification,etherification, acetalization or grafting. Such “protected” derivativesat Cl, which cannot be used as “monosaccharides” in the context of thepresent invention, consist, for example, of methyl α-glucopyranoside,isopropyl α,β-D-glucopyranoside, α-D-glucose pentaacetate orα,β-D-glucopyranosyl phosphate. The electrochemical oxidation of suchderivatives generates uronic acids, i.e. monocarboxylic materials thatonly have oxidized the primary alcohol functional group carried by thecarbon C6 of the glucose.

The production of such uronic acids by electrochemical oxidation ofmonosaccharides is widely described in the literature and in patent EP 1027 931 and the following papers:

-   -   “Catalytic oxidation of sugars by 4-(acetylamino)-TEMPO”, K. Ito        et al., Proc. Electrochem. Soc., 1993, Vol. 93-11, pp. 260-267,    -   “Electroorganic Synthesis 66: Selective Anodic Oxidation of        Carbohydrates Mediated by TEMPO”, K. Schnatbaum et al.,        Synthesis, 1999, No. 5, pp. 864-872.

In the context of the present invention, any constituent of themonosaccharide composition that undergoes an electrochemical oxidationstage can be chosen from the group consisting of:

-   -   aldohexoses, such as glucose, mannose, galactose or gulose,    -   aldopentoses and aldotetroses, such as ribose, arabinose,        xylose, erythrose and threose,    -   ketoses, such as fructose, tagatose, sorbose and xylulose,    -   the monosaccharides resulting from the hydrogenation of the        abovementioned products, such as sorbitol, mannitol, galactitol,        xylitol, ribitol, arabitol, erythritol and threitol,    -   the monosaccharides resulting from the oxidation of the        abovementioned products, such as gluconic acid, ketogluconic        acids, glucaric acid, galactonic acid, xylonic acid or        arabinonic acid, and their corresponding lactones and salts,    -   the other derivatives of the abovementioned products, provided        that they are not “protected” at Cl in the way indicated above.        It can be, for example, 3-methoxyglucose.

Despite not being favoured, the monosaccharide composition used asstarting material in the invention can comprise low percentages ofproducts other than monosaccharides, such as di-, oligo- andpolysaccharides or their derivatives.

Preferably, the monosaccharide composition comprises at least 80% byweight (dry/dry) of monosaccharide(s). For instance, the compositionsmay comprise 100% by weight (dry/dry) of glucose or 100% by weight(dry/dry) of a mixture of glucose and of gluconic acid or one of itssalts or 100% by weight (dry/dry) of 5-ketogluconic acid or 100% byweight (dry/dry) of sorbitol or of threitol.

The salts of oxidized monosaccharides, such as, sodium or potassiumgluconates, ketogluconates or glucarates, increase the conductivity ofthe reaction medium and, thus replacing sodium bromide.

The term “amine oxide”, is understood as any compound disclosed inpatents EP 780 399, EP 798 310 or EP 1 027 931 and which can be used asoxidation catalysts.

The electrochemical oxidation treatment of the monosaccharidecomposition can be carried out in any way accessible to a person skilledin the art. Preferably, according to the general methods or somealternative disclosed in the abovementioned patent EP 1 027 931 and/orthe abovementioned paper by K. Ito, as regards:

-   -   the nature of the catalyst (amine oxide) employed, which can        consist of TEMPO or derivatives of the latter, optionally        absorbed in all or part on a support,    -   the reaction temperature, which can be less than 30° C.,        preferably between 1 and 20° C.,    -   the nature of the cathode of the electrooxidation device, which        can be based on platinum, titanium, stainless steel or a carbon        material.

According to an essential characteristic of the invention, the anodeused for the oxidation of the monosaccharide composition is preferablybased on a carbon material.

The term “carbon material” includes crystalline carbon, such asgraphite, or amorphous carbon, such as charcoal and its activated forms.This material can be used in the form of rod(s), beads, plates, grids,felts or pads.

Furthermore, the catalyst (amine oxide) can, in all or part, beimmobilized on, adsorbed on or absorbed on this actual material prior tothe oxidation stage.

Advantageously, and in particular out of concern for productive output,this material has a high specific surface, i.e. at least equal to 0.10m²/g, preferably at least equal to 0.20 m²/g. It can be, by way ofexamples, a granular active charcoal or carbon felt, such as that of“Norit AX 08” type.

More preferably, said material can have a specific surface at leastequal to 0.25 m²/g.

Surprisingly and unexpectedly, the Applicant Company has found that, theuse of a carbon-based anode in a system without sodium hypochloritemakes it possible to obtain high yields of dicarboxylic materials, suchas glucaric acid and its salts, i.e. of greater than 50% and preferablyof greater than 90%.

The result is noteworthy because these yields can be obtained within arelatively wide range of pH values, i.e. of between 11 and 14, thusincluding pH values equal to or greater than 12, which were neverexemplified in the abovementioned prior art.

Alternatively, the electrochemical oxidation treatment is carried out ata pH of between 10 and 14, preferably of between 11.5 and 14.

More surprisingly, the method of the invention makes it possible todirectly obtain, i.e. without a purification stage, polycarboxyliccompositions which comprise significant contents of both dicarboxylic(for example, of glucaric acid and/or its salts) and tricarboxylicmaterials. The content of tricarboxylic materials can advantageously beof between 3 and 50% by weight (dry/dry).

According to an embodiment of the invention, the polycarboxyliccomposition obtained after the electrochemical oxidation of themonosaccharide composition comprises:

-   -   from 30 to 90% of one or more products chosen from dicarboxylic        acids and their salts, and    -   from 3 to 50% of one or more products chosen from tricarboxylic        acids and their salts, these percentages being expressed as dry        weight with respect to the total dry weight of said composition.

To the knowledge of the Applicant Company, the production frommonosaccharide compositions of these compositions, including thepolycarboxylic compositions in which the dicarboxylic component iscomposed of glucaric acid and/or of its salts, has never been achievedor even described.

As all compositions obtained by the method of the invention, thesecompositions may be advantageously used as novel industrial products inthe following industries: detergents and cleaning agents, watertreatment, metal treatment, plant treatment, fiber treatment, inparticular textile fibers or paper fibers, hydraulic binders, adhesives,founding, paints or leather. These compositions can also be used in thefood, pharmaceutical or cosmetic industries.

Thanks to the method of the invention, it is possible to obtain fromhexoses, polycarboxylic compositions that comprise, a compound of novelstructure having three carboxylic functional groups and six carbonatoms, in the free acid form and/or in the form of (a) salt(s).

After lengthy research and analytical studies, the Applicant Company issuggesting to name “2-carboxy-2,3,4-trihydroxypentanedioic acid” thecompound having the following general planar formula:

wherein:

-   -   each of the 3 components “X” can be chosen from the group        consisting of hydrogen, metals, preferably alkali metals and        alkaline earth metals, amino groups, preferably the ammonium        group, alkyl groups, preferably ethyl and methyl, and silyl        groups, and    -   each of the OH groups carried either by the carbon atom C_(d) or        by the carbon atom C_(e) can lie either to the right or to the        left of the carbon backbone.

According to the possible position of each of these two specific OHgroups, this compound is disclosed for each of the four isomers (1),(2), (3) and (4) as described below (for which each component “X” is asdefined above) and also for any mixture of at least any two of theseisomers.

Depending on the nature of the monosaccharide composition employed, themethod of the invention makes it possible to obtain polycarboxyliccompositions comprising:

-   -   either only one of the four isomers described above, for example        solely the isomer (1) when the monosaccharide composition is a        D-galactose or D-5-ketogluconic acid composition or solely the        isomer (2) when a D-fructose, D-mannose or D-2-ketogluconic acid        composition is concerned,    -   or a mixture in all proportions of at least two of the four        isomers described above, for example a mixture predominantly        comprising the isomer (1) and to a minor extent the isomer (2)        when a D-glucose composition is concerned.

To the knowledge of the Applicant Company, none of these isomers hasever been synthesized, or even identified in the abovementioned priorart. Therefore, it should be emphasize that none of these isomers hasever been listed by Chemical Abstract Service (CAS) and thus does nothave a “CAS” registration number.

Among the various ways of oxidating hexoses by chemical orelectrochemical route, only the claimed method combining 1) the absenceof NaOCl and 2) an electrochemical oxidation in the presence of acarbon-based anode can generate at least one of the isomers of2-carboxy-2,3,4-trihydroxypentanedioic acid, in the free form, in theform of (a) salt(s) and/or in other forms.

The Applicant Company has not observed the formation of the acid or ofits salts by substituting the anode with an anode based on othermaterials, in particular based on stainless steel.

The method of the invention makes it possible to obtain, with goodyields, polycarboxylic compositions having high content of productswhich are simultaneously “overoxidized” (di- or tricarboxylated) andnondecomposed, i.e. comprising the same number of carbon atoms than thatof the starting monosaccharide.

When applied to hexoses at a pH approximately of between 12 and 13.5,the electrochemical oxidation treatment of the invention, makes itpossible to directly obtain polycarboxylic compositions as describedabove for which the total content of glucaric acid (in the free acidform and/or its salts) and 2-carboxy-2,3,4-trihydroxypentanedioic acid(in the free acid form and/or in the form of salts) is at least equal to90%, this percentage being expressed as total dry weight of saidproducts with respect to the total dry weight of the composition.

When said method is carried out at a pH of approximately between12-13.5, a portion of the gluconic acid, optionally used as a startingmaterial but more generally obtained as an intermediate product fromglucose, is first significantly and rapidly converted to glucaric acidbefore significantly but gradually (for example, in 15 hours) convertedto 2-carboxy-2,3,4-trihydroxypentanedioic acid. This is probablyachieved by successive rearrangements probably involving 5-ketogluconicand 2-ketogluconic acids as some of the intermediates and generatinglittle or no decomposition products comprising from 2 to 5 carbon atoms.

In addition, it is noteworthy to record, as the Applicant Company hasobserved, that the effects or results generated by the method of theinvention and disclosed above can be obtained both in the presence andin the absence of sodium bromide, which is a precursor of thecooxidizing agent. The use of sodium bromide is widely recommended inthe prior art during the (electro)chemical oxidation treatment. Howeverlike NaOCl, it generates undesirable halogenated entities.

The present invention will be described in even more detail in thefollowing examples which are in no way limiting.

EXAMPLE 1

170 ml of osmosed water (2 Mohm.cm), 20 g (0.099 mol) of D-glucose inthe form of dextrose monohydrate and 80 mg (0.51 mol) of “TEMPO”(2,2,6,6-tetramethyl-piperidinyloxy) are introduced into an electrolysisreactor connected to a system for controling pH and temperature andequipped with an anode composed of a carbon felt with a thickness of 5mm and a specific surface of 0.3 m²/g, supplied by Carbone-Corrbine, andwith a cathode based on stainless steel.

Electrolysis is carried out at constant intensity (600 mA), thetemperature of the reaction medium being maintained between 2 and 5° C.and the pH being regulated at 12.2 using a 4M potassium hydroxidesolution. The electrolysis voltage (between anode and cathode) variesfrom 5V at the beginning of electrolysis to 3V at the end of thereaction. Electrolysis is halted when the amount of electricitydelivered corresponds to 125% of the theoretical amount necessary forthe oxidation of the glucose to glucaric acid (6 mol of electrons permole of glucose).

The composition obtained directly on conclusion of this electrochemicaloxidation stage (hereinafter “Composition 1”) is concentrated to 100 mlunder vacuum and then brought to pH 3.8 by gradual addition of AmberliteIR-120 resin. The medium is stirred at ambient temperature for 1 hour.

The precipitated material and the resin are filtered off through asintered glass funnel of porosity 4.

The resulting filtrate is brought to pH 9 by addition of 4M potassiumhydroxide solution and evaporated to dryness under vacuum (*), and theresidue is then dried under vacuum (*) at 50° C. 9.9 g of a white solidmaterial (hereinafter “Composition 1A”) are thus obtained.

The mixture of precipitated material and of resin is taken up in 60 mlof osmosed water (2 Mohm.cm) and its pH is brought to 9 by addition of4M potassium hydroxide solution. The resin is subsequently removed byfiltration under vacuum.

The resulting filtrate is evaporated to dryness under vacuum (*) and theresidue is then dried under vacuum (*) at 50° C.

(*) under a pressure of 14 mm of mercury (14 mmHg)

21.5 g of a white solid material (hereinafter “Composition 1B”) are thusobtained.

Compositions 1, 1A and 1B were analyzed by gas chromatography on acapillary column after persilylation. The entities are located by theirretention time and are quantified by using an internal standard andreference compounds.

The structures and the identities of some entities were investigatedusing:

-   -   mass spectrometry coupled to gas chromatography, several types        of derivatives being used and electron impact mode or chemical        ionization mode being employed,    -   ¹H and ¹³C nuclear magnetic resonance spectrometry.

The analytical techniques used were those described in theabovementioned paper by M. Ibert.

After numerous research studies and qualitative and quantitativeanalytical studies, the Applicant Company found that Composition 1Bcomprised by weight (dry/dry), approximately:

-   -   93.7% of potassium glucarate,    -   0.3% of potassium gluconate,    -   0.3% of potassium tartrate,    -   0.3% of potassium tartronate,    -   0.5% of potassium oxalate, and    -   5.0% of a potassium salt of a hitherto unknown tricarboxylic        acid (hereinafter “Product X”).

For its part, Composition 1A comprised by weight (dry/dry),approximately:

-   -   65.2% of said Product X in its tripotassium salt form,    -   18.2% of potassium glucarate,    -   2.5% of potassium gluconate,    -   2.4% of potassium tartrate,    -   3.5% of potassium tartronate and    -   8.2% of potassium oxalate.

For its part, Composition 1, obtained directly on conclusion of theelectrochemical oxidation stage and therefore in no way purified,comprised in particular approximately 70% by weight (dry/dry) ofpotassium glucarate and 24% by weight (dry/dry) of said Product X in itstripotassium salt form.

After numerous other research studies, the Applicant Company succeededin purifying the Product X present in Composition 1A.

Said composition, brought to a dry matter of 29%, was treated on acolumn of resin of “PCR 532” type in the H⁺ form, then brought to pH 9using a 2M potassium hydroxide solution and precipitated by employing asaturated calcium chloride solution. After filtration, the precipitatewas again brought to its acid form by addition of resin of “CA 200” typeuntil completely redissolved.

The resin was subsequently removed by filtration and the filtrate,brought to pH 9 using a 2M potassium hydroxide solution, was evaporatedto dryness.

Product x (“2-carboxy-2,3,4-trihydroxypentanedioic acid”) was thuscompletely purified, as it happens in the potassium tricarboxylate form.

Numerous additional analytical studies then made it possible to be ableto observe that said Product X was in fact composed of a mixturepredominantly comprising (>80% by weight, as dry/dry) the isomer (1)described above and comprising, as minor product (<20% by weight,dry/dry), the isomer (2) described above.

Furthermore, electrooxidation tests on D-glucose in the presence ofTEMPO were carried out under the same conditions as those describedabove, apart from the fact that the anode based on carbon felt wassubstituted by an anode composed either of stainless steel rods or of astainless steel pad.

Surprisingly and unexpectedly, it was observed, after electrolyzingunder these conditions for 24 hours, that

-   -   1) the anode composed of stainless steel rods did not allow        substantial conversion of the glucose, and    -   2) the anode composed of a stainless steel pad made possible a        low conversion of the glucose, this conversion generating        essentially decomposition products, such as oxalic and tartaric        acids.

In any event, in both cases, the Applicant Company did not observe theformation of any isomer of 2-carboxy-2,3,4-trihydroxypentanedioic acidor of any salt of such a product.

EXAMPLE 2

Moreover, the Applicant Company tested the effectiveness of Composition1A as detergency cobuilder in a compact powder formulation comprising25% by weight of zeolites.

It was found that said Composition 1A could be used effectively here forits ability to reduce the precipitation of calcium and magnesium salts,this being the case both at 20° C. and at 40° C. or 60° C.

For this purpose, Composition 1A proved to be overall more effective,for example, than commercial synthetic complexing agents, such as sodiumsalts of iminodisuccinic acid (“IDS”) or ethylenediaminedi-succinic acid(“EDDS”).

In addition, it was observed that Composition 1A could, within the samecompact detergent powder, be advantageously used in combination withother cobuilders, such as sodium tripolyphosphates or phosphonates.These combinations showed synergistic effects in terms of reduction inthe precipitation of calcium and magnesium salts.

Furthermore, Composition 1A proved to be useful as stabilizing agent forhydrogen peroxide employed in the treatment of paper pulps. This arosebecause of its capacity to complex with copper, which is less able todecompose the hydrogen peroxide.

EXAMPLE 3

The tests of Example 3 were carried out according to the generalspecifications of example 1 with a) an excess amount of current of 20%at 600 mA and an electrolysis time of 6 h 30 were used and b) thereaction pH was varied between 11 and 13.5 in increments of a pH unit of0.5.

For each reaction pH studied, the levels, expressed as % (dry/dry) andas product in the acid form, of the following 4 products were measured:

-   -   gluconic acid (hereinafter “Acid A”),    -   glucaric acid (hereinafter “Acid B”),    -   2-carboxy-2,3,4-trihydroxypentanedioic acid (herein-after “Acid        C”),    -   oxalic acid (hereinafter “Acid D”).

The results below were obtained, the figures after the decimal pointbeing rounded up to the higher percent for those at least equal to 0.50and being rounded down to the lower percent for those below 0.50.

pH Level (%) 11 11.5 12 12.5 13 13.5 Acid A 13 6 3 2 1 0 Acid B 57 68 7776 78 82 Acid C 23 21 17 18 16 10 Acid D 4 2 1 2 3 2

Another series of tests was carried out under the same conditions asthose described above apart from the fact that, in addition, sodiumbromide (NaBr) was introduced into the starting reaction medium. Thesodium bromide was present in an amount corresponding to 50% (dry/dry)of the amount of glucose employed.

Overall, over the pH range studied, the same amounts and the samechanges in the respective levels of each of the four acids were obtainedas those observed in the absence of NaBr.

In addition, a test carried out at a pH of 10.5 in the presence of NaBrmade it possible to obtain a polycarboxylic composition comprising inparticular approximately (dry/dry) 25% of gluconic acid (Acid A), 37% ofglucaric acid (Acid B), 22% of 2-carboxy-2,3,4-trihydroxypentanedioicacid (Acid C) and 7% of oxalic acid (Acid D), the remainder beingessentially composed of tartronic and tartaric acids.

These results show that the method of the invention makes it possible toobtain, starting from monosaccharide compositions, polycarboxyliccompositions with high content of overoxidized (di- or tricarboxylated)and nondecomposed products, in which:

-   -   the total content (dry/dry) of glucaric acid is at least 50%,        preferably at least 70%, and/or    -   the content (dry/dry) of glucaric acid and of        2-carboxy-2,3,4-trihydroxypentanedioic acid is at least 80%,        preferably at least 90%.

It is surprising to observe that such yields ofoveroxidized/nondecomposed products can be obtained within a relativelywide range of reaction pH values, i.e. between 11 and 14.

In addition, it is noteworthy to emphasize that, for pH values equal toor greater than 12, preferably of between 12 and 13.5, it is possible toobtain simultaneously a) a content of glucaric acid exceeding 75%(dry/dry), for example from 77 to 82%, and b) a total content ofglucaric acid and 2-carboxy-2,3,4-trihydroxypentanedioic acid exceeding90% (dry/dry), for example from 92 to 94%.

The same general observations were made when “TEMPO” was substituted byits derivatives, such as:

-   -   4-acetylamino-2,2,6,6-tetramethylpiperidinyloxy,    -   4-methoxy-2,2,6,6-tetramethylpiperidinyloxy,    -   2-hydroxymethyl-7,7,9,9-tetramethyl-1,4-dioxa-8-azaspiro[4.5]decan-8-oxy,    -   2-methoxymethyl-7,7,9,9-tetramethyl-1,4-dioxa-8-azaspiro[4.5]decan-8-oxy,    -   7,7,9,9-tetramethyl-1,4-dioxa-8-azaspiro[4.5]-decan-8-oxy.

The same general observations were made using a device of “Priam 1-2C”type, as sold by Socem-Elec, as electrochemical reactor.

Furthermore, additional tests targeted at substituting the D-glucose(hexose) by a pentose, as it happens D-xylose, D-arabinose or D-ribose,or by a tetrose, as it happens a hydrogenated tetrose, such asD,L-threitol, have confirmed the production of polycarboxyliccompositions comprising:

-   -   predominantly, the corresponding dicarboxylated/nondecomposed        product, for example xylaric acid from D-xylose, and    -   as minor product, a tricarboxylated but also nondecomposed        product, i.e. thus comprising the same number of carbon atoms as        the starting monosaccharide.

EXAMPLE 4

These tests were carried out according to the general specifications ofexample 1 apart from the fact that, in the present case, the D-glucosewas substituted by various monosaccharide compositions.

The type or types of isomer of 2-carboxy-2,3,4-trihydroxypentanedioicacid obtained in the reaction medium after electrooxidation is/are givenin the table below according to the component or components constitutingthe dry matter of the starting monosaccharide composition, it beingunderstood that:

-   -   “1” means the isomer (1) as described above,    -   “2” means the isomer (2) as described above,    -   “3” means the isomer (3) as described above,    -   “4” means the isomer (4) as described above,    -   by way of example, “1+2” means a mixture of “the isomer (1)” and        of “the isomer (2)” as are described above,    -   “Na” means “sodium”,    -   “K” means “potassium”.

Isomer(s) Starting monosaccharide(s) obtained D-Glucose 1* + 2 L-Glucose3* + 4 D-Galactose  1 + 3 D-Mannose 2 D-Gulose 3* + 4 D-Fructose 2D-Sorbitol 1* + 2 D-Mannitol 2 Na gluconate 1* + 2 K glucarate 1* + 2 Na5-ketogluconate 1 Na 2-ketogluconate 2 D-Glucose/Na gluconate mixture1* + 2 *predominant isomer of the mixture of isomers

This table shows that the method of the invention makes it possible, toinfluence the content of each of the 4 isomers of2-carboxy-2,3,4-trihydroxypentanedioic acid, by varying the nature ofthe starting monosaccharide composition.

It should be noted that, in the case of a monosaccharide compositionbased respectively on D- or L-galactose, polycarboxylic compositions areobtained, by employing the method of the invention, in which the isomerobtained (respectively isomer (1) or isomer (3) —cf. table above) can beeasily separated from the dicarboxylic compound obtained in conjunction,because of the very low solubility in water of the dipotassium salt ofgalactaric acid (or mucic acid).

1. A polycarboxylic composition produced by subjecting a monosaccharidecomposition to an electrochemical oxidation treatment carried out in theabsence of sodium hypochlorite and in the presence of a) an amine oxideand b) a carbon-based anode, wherein said polycarboxylic compositioncomprises: from 30 to 90% of glucaric acid, in the free acid form and/orin the form of (a) salt(s), and from 3 to 50% of2-carboxy-2,3,4-trihydroxypentanedioic acid, in the free acid formand/or in the form of (a) salt(s).
 2. A polycarboxylic compositionproduced by subjecting a monosaccharide composition to anelectrochemical oxidation treatment carried out in the absence of sodiumhypochlorite and in the presence of a) an amine oxide and b) acarbon-based anode, wherein said polycarboxylic composition comprisesglucaric acid and 2-carboxy-2,3,4-trihydroxypentanedioic acid, and intotal at least 90% of glucaric acid and of2-carboxy-2,3,4-trihydroxypentanedioic acid, this percentage beingexpressed as total dry weight of said products with respect to the totaldry weight of said composition.
 3. A method for preparing thepolycarboxylic composition according to claim 1, said method comprisingsubjecting a monosaccharide composition to an electrochemical oxidationtreatment carried out in the absence of sodium hypochlorite and in thepresence of a) an amine oxide and b) a carbon-based anode.
 4. The methodas claimed in claim 3, wherein said anode is based on a carbon materialhaving a specific surface at least equal to 0.10 m²/g, preferably atleast equal to 0.20m²/g.
 5. The method as claimed in claim 4, whereinsaid carbon material has a specific surface at least equal to 0.25m²/g.6. The method as claimed in claim 4, wherein said anode is selected fromthe group consisting of carbon felts and granular active charcoals. 7.The method as claimed in claim 3, wherein said electrochemical oxidationtreatment is carried out at a pH of between 10 to
 14. 8. The method asclaimed in claim 7, wherein the pH is between 11.5 and
 14. 9. The methodas claimed in claim 8, wherein the pH is between 12 and 13.5.
 10. Themethod as claimed in claim 3, wherein said electrochemical oxidationtreatment is also carried out in the absence of sodium bromide.